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From: Jian Cai <jiancai@google.com>
To: Will Deacon <will@kernel.org>
Cc: "Nick Desaulniers" <ndesaulniers@google.com>,
	"Manoj Gupta" <manojgupta@google.com>,
	"Luis Lozano" <llozano@google.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"David Laight" <David.Laight@aculab.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"James Morris" <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Andreas Färber" <afaerber@suse.de>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Marc Zyngier" <maz@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"David Brazdil" <dbrazdil@google.com>,
	"James Morse" <james.morse@arm.com>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH v4] ARM: Implement SLS mitigation
Date: Mon, 22 Feb 2021 13:50:06 -0800	[thread overview]
Message-ID: <CA+SOCLJVGJSn67VU24wPDdsOVeHhGe+KO5ekOCusano=bhn1Mg@mail.gmail.com> (raw)
In-Reply-To: <20210222115816.GA8605@willie-the-truck>

Please see my comments inlined below.

Thanks,
Jian

On Mon, Feb 22, 2021 at 3:58 AM Will Deacon <will@kernel.org> wrote:
>
> On Fri, Feb 19, 2021 at 03:08:13PM -0800, Jian Cai wrote:
> > This patch adds CONFIG_HARDEN_SLS_ALL that can be used to turn on
> > -mharden-sls=all, which mitigates the straight-line speculation
> > vulnerability, speculative execution of the instruction following some
> > unconditional jumps. Notice -mharden-sls= has other options as below,
> > and this config turns on the strongest option.
> >
> > all: enable all mitigations against Straight Line Speculation that are implemented.
> > none: disable all mitigations against Straight Line Speculation.
> > retbr: enable the mitigation against Straight Line Speculation for RET and BR instructions.
> > blr: enable the mitigation against Straight Line Speculation for BLR instructions.
> >
> > Links:
> > https://reviews.llvm.org/D93221
> > https://reviews.llvm.org/D81404
> > https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
> > https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/frequently-asked-questions#SLS2
> >
> > Suggested-by: Manoj Gupta <manojgupta@google.com>
> > Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
> > Suggested-by: Nathan Chancellor  <nathan@kernel.org>
> > Suggested-by: David Laight <David.Laight@aculab.com>
> > Suggested-by: Will Deacon <will@kernel.org>
> > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > Signed-off-by: Jian Cai <jiancai@google.com>
> > ---
>
> Please can you reply to my previous questions?
>
> https://lore.kernel.org/linux-arm-kernel/20210217094859.GA3706@willie-the-truck/
>
> (apologies if you did, but I don't see them in the archive or my inbox)

I should have clarified the suggested-by tag was in regard to the
Kconfig text change. Regarding your earlier questions, please see my
comments below.

> So I think that either we enable this unconditionally, or we don't enable it
> at all (and people can hack their CFLAGS themselves if they want to).

Not sure if this answers your question but this config should provide
a way for people to turn on the mitigation at their own risk.

> It would be helpful for one of the Arm folks to chime in, as I'm yet to see any
> evidence that this is actually exploitable. Is it any worse that Spectre-v1,
> where we _don't_ have a compiler mitigation?

> Finally, do we have to worry about our assembly code?

I am not sure if there are any plans to protect assembly code and I
will leave it to the Arm folks since they know a whole lot better. But
even without that part, we should still have better protection,
especially when overhead does not look too bad: I did some preliminary
experiments on ChromeOS, code size of vmlinux increased 3%, and there
were no noticeable changes to run-time performance of the benchmarks I
used.

  reply	other threads:[~2021-02-22 21:51 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-12  5:14 [PATCH] ARM: Implement Clang's " Jian Cai
2021-02-12  5:55 ` Nathan Chancellor
2021-02-12 10:41   ` David Laight
2021-02-12 19:52     ` [PATCH v2] " Jian Cai
2021-02-17  9:49       ` Will Deacon
2021-02-17 11:05         ` David Laight
2021-03-25 14:01         ` Linus Walleij
2021-02-17 18:20       ` Nick Desaulniers
2021-02-19 20:18       ` [PATCH v3] ARM: Implement " Jian Cai
2021-02-19 20:30         ` Nathan Chancellor
2021-02-19 23:08         ` [PATCH v4] " Jian Cai
2021-02-21 10:13           ` Russell King - ARM Linux admin
2021-02-22 11:58           ` Will Deacon
2021-02-22 21:50             ` Jian Cai [this message]
2021-02-23 10:04               ` Will Deacon
2021-03-03 15:18                 ` Linus Walleij
2021-03-03 15:29                   ` David Laight
2021-03-03 15:31                     ` Linus Walleij
2021-02-23  2:31           ` [PATCH v5] " Jian Cai
2021-02-23  2:35             ` Jian Cai
2021-03-03 15:04               ` Linus Walleij
2021-03-04 23:22                 ` Jian Cai
2021-03-06 12:25                   ` Linus Walleij
2021-03-10  4:43                     ` Jian Cai
2021-03-22 11:45                       ` Linus Walleij
2021-03-23 22:39                         ` Jian Cai
2021-03-05  0:53               ` [PATCH v6] " Jian Cai
2021-03-05  9:52                 ` Will Deacon
2021-03-06 12:27                   ` Linus Walleij

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